As law enforcement agencies attempt to piece together what happened this morning at the Washington Navy Yard, the public’s attention is shifting to security rules at Naval Sea Systems Command headquarters, a high-security building in the middle of the prestigious yard that is home to the Navy’s top officer and other admirals.

The headquarters, Building 197, contains classified and highly sensitive information about technical details of Navy ships and weapons, and it is closely guarded.

Visitors must first get access to the Washington Navy Yard with a military or civilian photo ID. The building is three blocks from the main gate. Those entering must go through an automated turnstile by flashing their NAVSEA badge. They are not allowed to bring in cellphones or photographic and recording devices, which can be exploited by foreign intelligence.

After passing through the turnstile overseen by the security guards at a desk, an employee can enter the lobby, which rises up to the building’s four-story height.

Guests must be checked in and turn in any recording devices. On a recent visit in June, a Navy Times reporter was required to lock his cellphone in a small locker outside the turnstiles before entering. The guest was not made to go through a metal detector but was constantly escorted by a staff member.

These security rules are comparable with those at the Pentagon. However, the Pentagon appears to have more armed guards, including those carrying assault rifles and monitoring those who access the building.

As with most bases, authorized personnel carrying bags are subject to random searches. But it is possible that a suspect who showed proper ID would not have had their bag checked. That may have been the case for this incident. Federal officials have identified the dead Navy Yard shooter as Aaron Alexis, a 34-year-old contractor, USA Today reports, who could have had ID-card access because of his job.

There is a cafeteria on the first floor. The fourth floor hosts the executive suite of Vice Adm. William Hilarides, the head of NAVSEA, who took over in June. His office overlooks the Potomac River.

Once through the initial security in the lobby, no additional checks are required to get to that floor, which can be reached by elevators or stairs.

It is unclear how much training the NAVSEA employees, who number about 3,000 and are primarily civilians, received on how to respond to a shooter scenario.

Capt. Michael Graham, who has worked there in Building 197 since 2008, said he had never seen a shelter in place drill at NAVSEA. The shelter in place order came shortly after initial reports of the shooting.

“I’ve seen the normal fire drills things like that, but never a shelter in place drill,” said Graham. “Normally the drills you have are to get out of the building.”